by Tim Hamilton
A common point of contention in many projects is the location and size of the loudspeakers. So why do loudspeakers need to be big?
I’ve worked with many architects and owners over the years and in almost every project someone on the design team will ask me questions such as, “Why do the loudspeakers have to be so big?” “Can they be put off in the corner?” “Can they be recessed behind the wall?” “How about putting them up in the 50’ peak of the sanctuary?” and “Can you make them pretty?” These and many similar questions are often voiced and the temptation sometimes is give a short response or simply tell people, “no” and dictate that the speakers have to be in a certain place. But I have found that investing some time in educating the team goes a long way toward getting a great solution. It takes some diplomacy and finesse to have a helpful and productive discussion with architects, owners, and design team members to lay out and explain why the location and size of speakers is important, and if you can effectively and accurately discuss the issues, the benefits are great.
An often overlooked part of system design is educating the client and the design team. So, early in the design process it needs to be established just how important the sound system is to the project. A good designer has to make sure things have been explained to the critical stakeholders and that they understand the trade-offs and design choices – while also remembering that the audio system has to be a high priority for the client or it will not be prioritized in the space. As much as it pains me to admit it, there are times when the sound system is not the most important thing in the room. In these situations, the designer may have some flexibility in the size, format, and location of speakers. But many sound systems are crucial to the success of the project (if it’s important enough to reinforce with loudspeakers, it’s important for them to work well!). With these types of systems it pays to be able to defend the design. The problem is that most people on the design team don’t think the sound system is that important – until it doesn’t work in the space. Then it can become a big and expensive problem to try and fix and suddenly everyone else gets amnesia about the earlier conversations they had about the speakers looking nice and pretty!
So, how can we go about having these important conversations before there’s an issue? Let’s first assume we are working on a project where the sound system is “crucial” (i.e., a large church, auditorium, or other venue). The space is intended to be “nice” and you’re running into issues with aesthetics and the speakers. Someone is pushing back on the loudspeaker system design and wants the speakers smaller, or put in a less optimal location. Where do we start in explaining the design?
First, we need to talk about location. Sound should come from where the action is. It sounds more natural and the human brain doesn’t have to work as hard to make sense of things if the eyes can see the sound source (loudspeaker) and the “action” (the talker or performer generating the sound). The loudspeakers need to be low enough in the space for people in the front rows to see them in their vertical peripheral vision. A good rule of thumb for figuring this out is to sit in the front row, look at the source, and note if you can see the loudspeaker in your vertical peripheral vision. You can do this in the actual room if it’s already constructed, or you can do this in a model (EASE, SketchUp, Revit, etc.). If the loudspeakers are too high in the room, it starts to sound like a disembodied voice (or the “Voice of God”). You may still be able to hear the loudspeaker, but it takes more effort for the listener to follow along. Since our ultimate goal is clear and concise communication, anything that impedes this goal should be avoided. If the loudspeakers have to be pushed higher they can be supplemented with stage fill speakers, but many designers may consider this a compromise or coordination headache.
Second, we need to talk about size. Small speakers may be fine in small places, but bigger speakers are probably needed in big places (not just higher SPL, but also physical size). Honestly, there are many rooms that can be serviced by a simple 2-way speaker cabinet (or several cabinets) with a 1.5” driver attached to a small horn combined with a 12” or 15” woofer. But more complex rooms may require a loudspeaker with more size (longer throw to the back, highly reverberant, low ceilings, or other challenges). Here we’re not just talking about a bigger cabinet. We also need to get more control (or higher directivity or Q) – but a higher directivity device generally means that we make a trade off to a bigger device.
So, what provides control? The two basic ways to guide sound from loudspeakers are horns and stacking multiple drivers together. Horns are pretty well known – anyone who has used a megaphone understands the basic principle that a horn has the ability to direct sound in a certain direction. What many people outside the audio industry don’t fully understand is that the size of the horn directly influences the frequencies that can be controlled. A small horn can only effectively direct much higher frequencies, but a larger horn has the potential to direct frequencies much lower in the audio spectrum. The “magic” in loudspeaker designs is to figure out how to best mate the driver to the horn and then design the size and shape of the horn to best reproduce the audio. Our purpose here is to help stakeholders understand that bigger horns offer the possibility of controlling sound at lower frequencies. The “price” of that control is that bigger loudspeakers will have a larger aesthetic impact and bigger loudspeakers may also be more expensive.
The other main method for controlling sound is stacking multiple drivers next to each other. Many loudspeakers that we would define as “line arrays” or “column arrays” use this method to provide control — typically in the vertical plane. For a “line array,” typically the horizontal control is defined by the horn angles in the box (or the radiation pattern of the drivers) and the real effectiveness of the array is in the vertical control. The vertical control happens by the interactions and spacing between the drivers. The more drivers placed next to each other, the more the radiation pattern “collapses” and starts to narrow in the plane in which the drivers are placed. If you stack them vertically you get a narrowing of the projected sound in the vertical plane. How much vertical control the array is capable of providing is defined by the height, and the longer the array of drivers, the lower the frequency that can be effectively controlled. At the same time this can produce unwanted anomalies in some of the higher frequencies in the side lobes of the horizontal coverage pattern. The “magic” of the line array design is take multiple drivers and multiple types of drivers and have the final product sound great. But the point is that the more vertical size in the array, the more control it is potentially capable of delivering. Assuming that the speakers are well designed and are using physics effectively, a loudspeaker with a larger horn or a longer array of stacked drivers will control lower frequencies better. Of course, that doesn’t necessarily mean that it will sound better. It just means it has the potential to control better. You still need to use your ears to make sure it sounds good!
The goal in all of this is to provide a sound system that makes the client (the person or group who is writing the check) happy. If every client understood how sound works in these complex devices it would be fairly easy to convince them what type of loudspeaker would be best. For most projects and designs it tends to be a compromise of location, size, aesthetics, price, and performance that dictate what loudspeakers are ultimately used. Most clients don’t understand these complexities, so the system designer has to have enough knowledge of what the client is trying to achieve and also have the expertise and knowledge to explain things well enough so that the client and design team can work together to accurately assess how the loudspeaker will perform in the room, not just how it looks. th